This invention relates to a pneumatic hammer which has a piston reciprocating in a metal cylinder tube, dividing the latter into an upper and a lower cylinder chamber, a plastic housing which serves as an external casing and which has at least one exhaust outlet, a support block mounted in the housing and holding an upper end of the cylinder tube and an oscillating valve housed in the support block and supplied with pressurized air from the outside. The oscillating valve alternatively introduces pressurized air into the upper and lower cylinder chambers to impart a reciprocating motion to a piston accommodated in the cylinder tube. Motions of the piston in the one direction serve to supply a driving force, for example, by delivering blows to an anvil or an end face of a tool shaft. The pressurized fluid is guided to the lower cylinder chamber in a conventional manner by longitudinally extending flow channels provided in the cylinder wall. Since the cylinder is made of a hardenable steel by casting or forging and the cylinder bore as well as the channels are made by subsequent machining, the result has been a tool of substantial weight and significant expense.
U.S. Pat. No. 3,263,770 proposes to coat the metal cylinder which accommodates the working piston, with a thin layer of damping material, for example, of rubber or an elastomer along its entire length, and to surround closely the layer with a thin steel jacket. An exhaust muffler is provided for noise suppression.
U.S. Pat. No. 2,128,742 describes a tool wherein an outer body of insulating material is formed on the metal cylinder. An envelope constituted by a tube surrounds the mid portion of the cylinder and forms, together with the cylinder, an expansion chamber for receiving the fluid from the outlet opening of the cylinder. Annular plates are provided at the ends of the expansion chamber. A plurality of axial separating walls are arranged in a stepwise manner about the cylinder. One of the two separating walls is, on either side of the outlet opening, at a distance from the lower annular plate while the other separating wall is at a distance from the upper annular plate. Two further separating walls are arranged in a similarly offset manner and thus the outgoing fluid has to travel along two long paths to the exhaust in the envelope. This arrangement is intended to produce a damping effect.
European Pat. No. 15,700, to which correspond U.S. Pat. Nos. 4,303,131 and 4,303,133 describes a pneumatic hammer in which a cylinder tube accommodates a reciprocating piston and is surrounded by a rubber supporting body. In radial longitudinal ribs there are provided flow channels for supplying the fluid to the lower cylinder chamber. The upper cylinder chamber is directly supplied with pressurized air from an oscillating valve. A cylindrical noise suppressing (muffling) tube surrounds the cylinder along its entire length including the anvil and the tool holder. Between the noise suppressing tube and the rubber supporting body there is formed a noise suppressing chamber which is in communication with the environment by means of openings. According to a variant three ribs are provided, each being in contact with the noise suppressing tube and thus bound axially extending chambers. From the cylinder chamber there extend two gas outlets to two different chambers. These chambers are connected at the side oriented towards the tool bit with a further, third chamber with the intermediary of throttles. The third chamber is bounded by the ribs and is in communication with the external environment by means of an inner elongated port. In this manner, two damping chambers are connected in series. The noise suppressing chamber too, is of rubber so that all components forming chambers and flow channels are made of a formable material which reduces the overall weight of the tool, and further, the manufacturing costs may be maintained at a low level despite the use of an intricate noise suppressing arrangement.